KR100663301B1 - Die-casting method and die-cast products - Google Patents

Abstract

After the cavity 2 of the die casting mold 1 is evacuated to remove gas, oxygen is blown into the cavity 2 until the internal pressure of the cavity exceeds atmospheric pressure, and then the molten metal is released into the cavity 2. Is forced into it. The gas in the cavity 2 is aspirated through the suction nozzle 11 at a vacuum of less than 100 millibars. Oxygen is blown into the cavity 2 through the nozzle 11 to fill the cavity 2 with oxygen at an internal pressure higher than atmospheric pressure. If the molten metal 5 is injected into the cavity 2 purified in this manner, the content of gas is completely prevented. As a result, the die-cast product obtained can be used as a functional member as well as a structural member by removing defects such as blowholes or porosity generated by gas containing.

Die casting product, Die casting mold, Cavity, Sleeve, Inlet hole, Molten metal, Plunger rod, Suction nozzle, Oxygen nozzle

Description

Die casting method and die casting product {DIE-CASTING METHOD AND DIE-CAST PRODUCTS}

1 is a schematic view showing a die casting machine to which the present invention is applied;

2 illustrates blowing oxygen into the cavity of the die casting mold through the sleeve, and

3 illustrates the introduction of molten metal into the sleeve.

The present invention relates to a die casting method for a die cast product that can be used as a structural member as well as a functional member and relates to a die casting product produced by the method. In the conventional die casting method, molten aluminum or aluminum alloy (hereinafter referred to as molten metal) introduced into the sleeve is forcibly injected into the cavity of the die casting by the plunger. Most gases such as air and water vapor are removed from the cavity in response to the injection of molten metal, but some gas remains in the cavity after injection. Die casting molds designed specifically for thin-walled products or products with complex geometries have parts such as bottlenecks that impede gas flow, making it difficult to remove gas from the cavity completely.

Gas trapped in the cavity is contained in the diecast product when the injected molten metal cools and solidifies in the cavity. Therefore, die-cast articles obtained in this way are considered to be inadequate for functional use because of insufficient mechanical properties, which are for example scrolls, pistons, cylinder blocks, connecting rods or suspension parts. When casting defects arising from the gas content are solved, a die casting method excellent in productability can be applied to various technical fields.

Vacuum diecasting methods have been proposed to eliminate adverse effects resulting from gas content. According to the vacuum die casting method, the gas in the cavity of the die casting mold is evacuated before the molten metal is injected to remove the gas from the cavity. The cavity is maintained at a vacuum degree in the range of 200 to 500 millibars by vacuum aspiration. However, the internal pressure of the cavity cannot be reduced below this value due to the ingress of air through the narrow gap of the die. Air intrusion also occurs during the introduction of molten metal into the sleeve. As a result, casting defects such as porosity caused by the gas content are also detected in the product obtained by the vacuum die casting method even if the gas content is slightly reduced in comparison with the product obtained by the conventional die casting method. In this regard, the product is not good enough for use as a functional member.

Oxygen die casting methods have been developed to eliminate the drawbacks of vacuum die casting methods. According to the oxygen die casting method, as disclosed in Japanese Patent Laid-Open No. 50-21143, the cavity of the die casting mold is filled with oxygen at a pressure higher than atmospheric pressure to replace the gas with oxygen before injecting the molten metal. Since oxygen transported into the cavity flows out through the narrow gap of the die as well as the inlet hole, intrusion of atmospheric gas (air) through the narrow gap or inlet hole is prevented. In addition, the oxygen transferred into the cavity reacts with the dissolved metal and the reaction product Al ₂ O ₃ is dispersed as fine particles in the cast product without adversely affecting the obtained diecast product.

However, complete replacement of the gas from the cavity of the die casting mold by oxygen injection is practically impossible even when oxygen is transported into the cavity at a pressure higher than atmospheric pressure. The gas remains in the cavity where it is difficult to replace. Die-casting molds designed to produce products with complex geometries have parts that are difficult for oxygen to reach so that gases such as air and steam cannot be replaced by the transported oxygen and so remain. Residual gas from the releasing agent is contained in the product causing defects.

Residual air is efficiently removed from the cavity by oxygen blowing during vacuum aspiration, as disclosed in Japanese Patent Publication No. 57-140. However, blowing oxygen at the same time as vacuum evacuation is not effective for removing water vapor. In fact, casting defects caused by gas content are still detected in cast products obtained by this method. Japanese Patent Application Laid-Open No. 1-46224 discloses another die casting method, and oxygen blowing is performed after vacuum suction. However, casting defects are still detected in the cast product because the cavity of the die casting mold is kept at a reduced pressure during oxygen blowing. The inclusion of trapped gases also causes blisters in the diecast product when the diecast product is heat treated with T6 treatment (ie, solid solution heating, quenching and then aging) to improve the mechanical properties. . A blister refers to a phenomenon in which a cast product or the like swells due to expansion of bubbles during heat treatment by bubbles or the like contained therein. To avoid these blisters, most diecast products are not heat treated.

The present invention aims to eliminate this problem as described above. It is an object of the present invention to significantly reduce the content of gases by combining the advantages of both vacuum die casting and oxygen die casting for die cast products usable as functional members.

The die casting method according to the present invention comprises the steps of drawing gas from the cavity of the die casting into a vacuum at a pressure of less than 100 millibars to remove gas containing water vapor from the cavity, blowing oxygen into the cavity, and the internal pressure of the cavity is at atmospheric pressure. It is characterized in that it comprises the step of forcing the molten metal when exceeding.

In this specification, gases such as air and water vapor, which are present in the cavity of the die casting mold and are incorporated into the product during the die casting operation, may cause defects such as blowholes in the product, collectively referred to as "gas". In addition, according to the present invention, pure oxygen blown to remove residual gas remaining in the cavity even after evacuating the gas is referred to as "oxygen" to distinguish it from the gas which adversely affects the die casting product.
First, the gas in the cavity of the die casting is aspirated with a vacuum of pressure less than 100 millibars. In particular, the gas is effectively released when the draft rate is 500 millibar / sec or more. The cavity is filled with oxygen at a pressure slightly above atmospheric pressure. When the internal pressure of the cavity exceeds atmospheric pressure, the injection of molten metal into the cavity begins.

Since molten metal is injected into the cavity maintained in this way, the gas trapped in the cast product is significantly reduced to levels below 1cc / 100g-Al. As a result, the obtained die cast product has excellent mechanical properties required for the functional member. In addition, die-cast products are thermally treated with a T6 treatment without blisters generated by trapped gases.

The gas contained in the die cast product is generated from the air remaining in the cavity of the die casting mold in the conventional die casting method. This residual air can be substantially reduced by vacuum or oxygen die casting. However, casting defects caused by trapped gases are unavoidable in die cast products obtained even when the residual air is significantly reduced. The inventors studied and investigated the effects of casting defects and causes from various properties on diecast products in which adverse effects resulting from residual air are eliminated by vacuum or oxygen die casting methods. As a result, the inventors have found that water that dilutes the release adhering on the inner surface of the die casting is the main cause of the occurrence of casting defects, and the influence of moisture on the casting defects increases as the residual air in the cavity decreases. When the gas in the cavity is evacuated, the moisture contained in the release agent is evaporated and released as vapor from the cavity. However, commonly used water-soluble release agents take some time to dry, even under vacuum. When only gas is evacuated from the cavity, evaporation of moisture can be limited to the surface of the release agent without evaporation inside the release agent and the release agent is not sufficiently dried. The generated water vapor also remains partly in the cavity and thus is included in the molten metal that is injected into the cavity.

The moisture contained in the release agent according to the invention is mostly released as vapor from the cavity of the die casting by vaccum evacuation and the release agent is sufficiently dried. Water vapor still remaining in the cavity diffuses into the oxygen and is released with oxygen from the cavity in a subsequent oxygen blowing step. The moisture contained in the release agent is completely released by the combination of oxygen blowing and vacuum suction, so that the gas content in the obtained die cast product is greatly reduced. Evaporation of moisture from the release agent is effectively enhanced when gas is drawn out of the cavity at a vacuum of pressure less than 100 millibars to dry the release agent. The extraction rate is preferably set to 500 millibars / sec or more. This high rate of absorption causes bumping of the moisture and thus rapid drying.

Before the molten metal is injected into the cavity of the die casting mold, the cavity is in a state of significantly reduced air and water vapor. As a result, the gas content in the diecast is greatly suppressed and the casting defects generated from the gas content of the product are eliminated.

In the die casting method, the sleeve 3 attached to the cavity 2 is connected to the die casting mold 1 as shown in FIG. 1. The sleeve 3 has an inflow hole 4 through which the molten metal 5 flows into the sleeve 3. The molten metal 5 in the sleeve 3 is pressurized by the tip 7 attached to the plunger 6 and forcedly injected into the cavity 2. After the cavity 2 is filled with the molten metal 5, the molten metal 5 is cooled and solidified into a profile formed by the inner surface of the die casting mold 1. The die cast product obtained in this manner is taken out from the die casting mold 1 by pressing the ejector pin 8 and the like in the cavity 2 after the die cast product is cooled.

According to the invention, the suction nozzle 11 is attached to the die casting mold 1 at a suitable position such as its separating part to connect the cavity 2 to the vacuum pump 12 through the suction nozzle 11. When the gas is evacuated from the cavity 2 through the suction nozzle 11, the ambient air can enter through the part into which the ejector pin 8 is inserted during the vacuum suction. This intrusion is prevented by sealing the gap between the ejector pin 8 and the die portion with a sealant 13. On the other hand, the inlet hole 4 is closed by the plunger tip 7 so that ambient air cannot enter the inside of the sleeve 3 through the inlet hole 4.

The oxygen nozzle 14 is opened into the sleeve 3 to blow oxygen into the cavity after vacuum aspiration. The oxygen nozzle 14 is connected to an oxygen supply source through an adjustment valve 15.

When gas from the cavity 2 is drawn out through the suction nozzle 11, gas such as air and water vapor is removed from the cavity 2 as well as the inside of the sleeve 3 connected with the cavity 2. Although the cavity 2 has a complicated shape, the gas is removed from all corners and corners of the cavity 2 by preferably adjusting the draft rate in the range of 500 millibar / sec or more. This high speed aspiration causes bumping of the moisture contained in the release agent attached to the inner surface of the die casting mold 1, resulting in a significant reduction in the water vapor from the cavity 2.

The vacuum suction is preferably continued for about 1 to 2 seconds under the condition that the inlet hole 4 is closed by the plunger tip 7. The suction time period is set relatively long in comparison with the conventional die casting method in which the gas in the cavity 2 is sucked out for a time period shorter than 1 second without closing the inlet hole 4. The cavity 2 is drawn off with a vacuum of less than 100 millibars due to the longer drawback period. Water vapor generated from the release agent attached to the inner surface of the die casting mold 1 is separated from the inner surface of the die casting mold and discharged to the outside.

The removal of water vapor is performed more effectively by vacuum aspiration as compared to blowing oxygen into the cavity because the gas stream flows faster in the cavity 2. However, when the cavity 2 is aspirated with insufficient vacuum at a pressure of 100 millibars or more, a relatively large amount of gas remains in the cavity 2. The large amount of gas remaining in the cavity 2 is not replaced by oxygen in the next oxygen blowing step and is often included in the cast product. On the other hand, if the cavity is aspirated with a vacuum of less than 100 millibars, the moisture contained in the release agent is rapidly evaporated and released out of the cavity 2 as water vapor. The decrease in moisture is greatly accelerated by the high velocity evaporation of 500 millibars per second or more, which causes bumping of the moisture. Bumping can evaporate moisture not only from the surface but also from the inside of the release agent, greatly reducing the remaining moisture. The upper limit of the extraction rate is about 800 millibars / sec in consideration of the effective capacity of the vacuum apparatus.

After vacuum aspiration, oxygen is blown into the cavity 2 through the nozzle 14. The oxygen supply is preferably continued for 3-4 seconds until gas and oxygen flow out through the separating part of the die casting mold 1. Since oxygen is blown into the cavity 2 under reduced pressure in the previous step, oxygen flows to all corners and corners of the cavity 2 as a high speed stream. Water vapor generated from the water contained in the release agent and remaining in the cavity 2 is diffused in the oxygen and released together with the oxygen outside the cavity 2. This effect of oxygen blowing in the removal of water vapor cannot be expected in any of the methods disclosed in Japanese Patent Laid-Open No. 57-140 and Japanese Patent Laid-Open No. 1-46224 in which oxygen is blown into a cavity maintained under reduced pressure.

The plunger tip 7 is retracted to open the inlet hole 4 during continuous blowing of oxygen. When the inlet hole 4 is opened, oxygen flows out through the inlet hole 4 as shown in FIG. The outflow of oxygen effectively suppresses the ingress of ambient air into the sleeve 3 through the inlet hole 4.

After the inlet hole 4 is opened, the molten metal 5 flows into the sleeve 3 from the ladle 16. Since oxygen is effectively discharged during the inflow operation, the outflow of oxygen effectively prevents the inflow of ambient air accompanying the molten metal (5).

The die casting mold 1 is preferably preheated to 150 ° C. to 200 ° C. before the inflow step to reduce the thermal shock caused by the inflowing molten metal 5 and improve the productability. The plunger rod 6 is advanced after the mass of molten metal 5 required in one cycle of die casting has entered the sleeve 3. The inlet hole 4 is closed by the forward movement of the plunger rod 6. Since the closed state does not introduce ambient air into the sleeve 3 through the inlet hole 4, the supply of oxygen can be stopped.

After gases such as air and water vapor have been completely removed from the interior of the cavity 2 and sleeve 3 as described above, the plunger rod 6 is advanced to forcibly inject the molten metal 5 into the cavity 2. Let's do it. The injected molten metal 5 is formed into a volume BULK having a profile that mimics the inner surface of the die casting mold 1. This volume is cooled and solidified into a die cast product having a predetermined shape. Then, blowholes or porosity generated by the gas content are not generated in the die cast product because gases such as air and water vapor are completely excluded from the cavity 2. Oxygen remaining in the cavity 2 reacts with the injected molten metal and the reaction product Al ₂ O ₃ is dispersed into fine particles in the diecast product without causing any adverse effects. Thus, the die cast product obtained in this way has excellent properties.

Example

The die casting mold 1 used in this example has a cavity 2 of 150 mm in diameter and 120 mm in length. Suitable water cooling means are provided in the die casting mold 1 to partially cool the die casting mold 1.

The release agent diluted with water after the cavity 2 has been cleaned by the air blow is sprayed on the inner surface of the die casting mold 1 for 5 seconds. The die casting mold 1 is then preheated to 180 ° C. and placed in a suitable position in the die casting machine. The periphery surrounding the ejector pins 8 is sealed with a sealant 13 and the suction nozzle 11 is attached to the separating portion of the die casting mold 1.

The inlet hole 4 is closed by the plunger tip 7, and the gas is drawn out from the cavity 2 at the suction speed of 700 millibars / sec through the suction nozzle 11 from the inside of the cavity 2 and the sleeve 3. . The vacuum gauge (not shown) provided to the vacuum system 12 represents 75 millibars.

After vacuum aspiration, the control valve 15 is opened to blow oxygen into the cavity 2 through the oxygen nozzle 14. Oxygen blowing continues until oxygen flows out through the separating portion of the die casting mold 1.

After the oxygen blowing continues for 3.5 seconds, the plunger tip 7 is retracted to open the inlet hole 4. Thereafter, the molten metal alloy ADC 12 prepared by conventional molten metal treatment is introduced into the sleeve 3 through the inlet hole 4. Oxygen is continuously blown into the sleeve 3 through the oxygen nozzle 14 while the molten metal 5 is introduced into the sleeve 3 for 5 seconds.

After the inflow is completed, the supply of oxygen is stopped and the plunger rod 6 is advanced to forcibly inject the molten metal 5 into the cavity 2. Injection of the molten metal 5 is completed in a short time of approximately 0.1 seconds.

It takes about 5 seconds to solidify the injected molten metal 5 in the die casting mold 1. After the die cast product is cooled, it is taken out from the die casting mold 1. The diecast product N0.1 obtained in this manner is subjected to a lansley test and a mechanical test to determine the gas content in the diecast product.

For comparison, the die cast product N0.2 obtained by the conventional vacuum die casting method from the same aluminum alloy and the die cast product N0.3 obtained by the conventional oxygen die casting method are subjected to the same lancel and mechanical test. In the vacuum die casting method, the gas in the cavity 2 is sucked out for 1.5 seconds before the injection of the molten metal 5. In the oxygen die casting method, oxygen is blown into the cavity 2 for 2 seconds and then molten metal 5 is injected into the cavity 2 for 5 seconds while blowing oxygen.

The test results are shown in Table 1. This shows in Table 1 that the gas amounts such as N ₂ and H ₂ in the die cast product N0.1 according to the present invention are extremely reduced in comparison with the values of the die cast products N0.2 and N0.3. The ductility and tensile strength of die cast product N0.1 is higher than the ductility and tensile strength values of die cast products N0.2 and N0.3. Diecast N0.1 is also produced by T6 treatment (ie, heated at 480 ° C for 3 hours, quenched with water and then aged at 160 ° C for 5 hours) without blistering due to extremely reduced gas impurities. Improve the mechanical properties.

Effect of Die Casting Method on the Properties of Die Cast Products Sample No. Die casting method Gas impurity amount (cc / 100g-Al) As casting After T6 treatment T.S. El. T.S. El. One The present invention 0.6 32 2.0 40 5.0 2 Vacuum die casting 6 23 0.8 Blister with 1-2 mm diameter 3 Oxygen Die Casting 2 27 1.5 Blister with 0.2-0.5mm diameter Note: T.S. means tensile strength (㎏ / ㎠). El. Means elongation (%).

Moreover, die casting was carried out under the same conditions except that the draft rate was varied within the range of 100 to 800 millibars / sec. Each diecast product is subjected to a Lansley test to determine the amount of residual gas. Significant reductions in residual gas occur at draft rates above 500 millibars per second. This result means that high-speed suction causes bumping of the moisture contained in the release agent adhered on the inner surface of the die casting mold and accelerates the removal of the moisture from the cavity 2.

As described above, according to the present invention, gases such as air and water vapor generated from a release agent attached to the inner surface of the die casting mold are die cast by oxygen blowing after vacuum suction until the internal pressure of the cavity exceeds atmospheric pressure. It is completely removed from the cavity of the mold. Since the molten metal is injected into the cavity in which the noxious gas is completely removed, the obtained diecast product does not contain defects such as blowholes or porosity generated by gases such as residual air or water vapor. Thus, this new diecasting method is applicable to the production of functional as well as structural members using the advantages of high productivity.

Claims (3)

In the method of die casting aluminum or aluminum alloy, Drawing the gas out of the cavity of the die casting mold with a vacuum of pressure less than 100 millibars to release the gas from the cavity, Blowing oxygen into the cavity until the internal pressure of the cavity exceeds atmospheric pressure, and Forcibly injecting molten aluminum or an aluminum alloy into the cavity, The gas in the cavity of the die casting mold is aspirated at a draft rate of 500 millibar / sec or more. delete A die cast product produced by the die casting method as defined in claim 1, wherein the die cast product contains gas impurities at a concentration of less than 1 cc / 100 g-Al.

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